textproduct: Rapid City

KEY MESSAGES

- Showers will continue to gradually decrease in coverage tonight.

- Areas of fog will continue through Monday morning. Reduced visibilty is expected around the Black Hills and across the western South Dakota plains for the Monday morning commute.

- More clouds than sun to start the week, followed by warmer and drier conditions later in the week.

UPDATE

Issued at 935 PM MDT Sun Sep 20 2026

Showers, low clouds, and fog are the big stories for the overnight hours.

The latest upper level low is still spinning and tracking eastward through the central states. This low has been bringing, and will continue to bring, bands of rain showers, drizzle, and low clouds to the area. Slowly, the rain showers will improve overnight but the drizzle and low clouds will last well into tomorrow/Monday.

The other challenge for tonight and tomorrow is the fog. Easterly winds will keep patchy fog and low visibility in and around the Black Hills and SD plains through tonight and into tomorrow. Some hi-res models keep fog in the SD plains through Monday afternoon. So there is some evidence that the fog, or low clouds, will linger through most of Monday.

DISCUSSION

(This Afternoon Through Saturday) Issued at 1144 AM MDT Sun Sep 20 2026

Water vapor and upper level analysis depicts a low centered over Wyoming, a ridge extending up the West Coast, and another low just off-shore of California. At the surface, the low is over the western Nebraska Panhandle with a weak trough extending northwestward along the Bighorns. Latest radar imagery has a large swath of rain over the western and central South Dakota plains, rotating counter- clockwise around the upper low.

For the rest of today, the main band of rain over the South Dakota plains will continue to lift northward, being replaced by a few smaller, less organized showers for the afternoon and evening hours. Rain showers across northeastern Wyoming will be less, as drier gets pulled up from southeastern Wyoming. High temperatures will remain cool with the damp conditions and abundant cloud cover, with no deviation from blended guidance which is close to current temps.

The upper low opens up and drifts east overnight, which will in-turn ends the rain showers from west to east. Lingering moisture in the air, combined with surface pressure rises and light winds, will result in areas of fog and low clouds into Monday morning. Visibility will gradually improve late Monday morning, with the lower ceilings and clouds sticking around throughout the day.

More clouds and some fog for MOnday night/Tuesday across the South Dakota Plains and the southern Black Hills - with the Northern Black Hills and portions of northeastern Wyoming becoming sunny. Clouds will gradually decrease across the entire area through the day, with increasing south-southeasterly winds. The strongest winds, 15 to 25 mph, will likely be across northwestern South Dakota where the pressure gradient looks to be the tightest.

A weak shortwave trough moves through Wednesday and Wednesday night, which could result in some showers across the area. The wave moves through fairly quickly, thus, some areas should remain dry.

A drier, warmer pattern then sets up for the end of the week into the weekend, with highs about 5 to 10 degrees above average.

AVIATION

(For the 06Z TAFS Through 06Z Monday Night) Issued At 1028 PM MDT Sun Sep 20 2026

Areas of light rain will accompany widespread IFR/LIFR CIGS and areas of MVFR/IFR VSBY (BR/FG) late tonight through Monday morning. Some gradual improvement is expected late Monday morning through the afternoon as fog dissipates, but MVFR/IFR CIGS are expected to linger through the rest of the forecast period (especially the Black Hills area). Light showers may also develop Monday afternoon, which could reduce VSBY to MVFR/IFR at times.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.